Tap changing system



y 1931. t. H. HILL 1,804,614

TAP CHANGING SYSTEM Filed July 14, 1928 Fig. 1.

INVENTOR Leland H. Hl'Z Z 7 A.TTORNEY Patented ay 12, 1931 mm D H. HILL 01 COLLING$WGGD, NEW JERSEY, ASSIGNOR T0 WESTINGHOUSE ELEC- TFJTC tit EMUFACTURTNG COMPANY,

A. COMORATION OF PENNSYLVANIA TA? CHANGING SYSTmd Application filed July .14,

My invention relates to electric transformers and more particularly to transformers having means associated therewith for changing the voltage ratio between the primary and secondary windings while the transformer is under load.

My invention has for an object to provide means for reducing the number of switches required to cover a wide range of voltage ratio changes in a number of small steps.

Another object of my invention is to provide means for simplifying and generally improving tap changing apparatus wherein small voltage ratio changes are necessary.

In general my invention comprises the use of auxiliary windings in. the main transformer for energizing an auxiliary Winding on the preventive auto transformer that is used with single winding tap changing schemes. The voltage ratio of the transformer between tap positions is modified by connecting one of the auxiliary windings in the main transformers in circuit relation with the auxiliary transformer and the preventive auto transformer. Auxiliary windings are provided in the main transformer to coact with the auxiliary winding in the preventive auto transformer to decrease or increase the voltage ratio.

My invention may be more readily understood if the following description is read with reference to the accompanylng drawings.

In the drawings:

Fig. 1 is a schematic diagram of a transformer having associated therewith voltage ratio changing apparatus constructed in accordance with my invention, and

Fig. 2 is a chart showing the sequence of operation of the tap changing switches of the device shown in Fig. 1.

Referring to Fig. 1, a transformer 1 comprising a primary winding 2 and a secondary winding 3 is provided with a voltage ratio changing apparatus 4 for operation, either when the transformer 1 is, or when it 1s not under load. The primary winding 2 preferably comprises the high voltage winding that is connected to the transmission line by terminals 5 and 6. The secondary winding 3 preferably comprises the low voltage wind- 1923. aerial Ito. 292,7?1.

ing. This is in turn connected to either generating or consuming apparatus by conduc= tors 7 and 8.

It is to be noted in connection with Fig. 1 that the terminal 8 is either solidly grounded, as shown, or it may be connected to another portion of the winding 3; that is, the tap changing equipment must either be com nected in the grounded end of the winding or in the middle of a delta connected winding.

The winding 3 is provided with a plurality of taps 8, 9, 10, 11, 12 and 13 that are connected in electric circuit relation to terminals of switches 14, 15, 16, 17 18 and 19, respectively. The other terminals of the switches are connected in circuit relation alternately to opposite terminals 20 and 21 of a preventive auto transformer 22. A mid terminal 23 on the auto transformer 22 is connected to the conductor 8. The switches 14, 16 and 18 are connected, by conductors 24, 25 and 26, to a' conductor 27 leading to the terminal 21 of the reventive auto-transformer 22. The remaining switches 15, 17 and 19 are connected, by conductors 28, 29 and 30, to a conductor 31 that is connected to the terminal 20 of the auto-transformer 22.

By closing the switches 14, 15, 16, 17, 18 and 19 in sequence so that at least one switch is always closed, the voltage ratio between the primary winding 2 and the secondary winding 3 may be increased or decreased.

The preventive auto transformer 22 is designed to carry the full load current from the secondary winding 3 in either half of its windings without excessive heating. When adjacent switches are closed each half of the winding of the auto transformer carries approximately half of the full load current of the secondary winding 3. For example, when switch 14 is closed, the lower half 32 of the winding of the preventive auto transformer 22 carries full load current. When both switches 14 and 15 are closed, part of the full load current is carried by the lower half 32' and part by the upper half 33 of the preventive auto transformer 22. When the switch 14 is opened and the switch 15 is closed the upper half 33 of the preventive auto transformer 22 carries the full load current.

In order to reduce the number of switches required to cover a wide range of. small voltage ratio steps, two auxiliary windings 34 and 35 are wound on the main core of the transformer 1. These auxiliary windings 34 and 35 are in turn connected in circuit relation with an auxiliary winding 36 on the preventive auto transformer 22 through switches 37 and 38, respectively, and conductors 39 and 40. The switches 37 and 38 are arranged so that the winding 36 may be energized either to decrease or increase the voltage ratio by means of the auto transformer 22; the auxiliary winding 36 being disposed on the same core with the main winding of the auto transformer 22.

Each of the windings 34 and 35 has a number of turns corresponding approximately to one-eighth of the number of turns of the portions of the secondary winding 3 between adjacent taps.

' and 35, preferably, each has one-fourth as many turns of the winding as the preventive auto transformer 22; that is, their ratio is 4 to l for the entire winding 22 or 2 to 1 for 1 one-half the winding. It is to be noted that such ratios depend upon design considerations and are set forth here for purposes of illustration.

The insertion of winding 34 or 35 in the circuit adds or subtracts one-fourth of the.

volt-age magnitude to. each half of the preventive auto transformer volt-age. By adding or subtracting the voltage of winding 34 or 35, an intermediate voltage may be obtained that is half way between the voltage of the prevailing tap position on the secondary winding 3 and the mid point of the preventive auto transformer.

Fig, 2' 'shows how the sequence of operation of the switches whereby the voltage ratio of the transformer is increased or decreased.

current. step switch 38 is closed. To make a further change, switch 15 is closed and 38 opened.

When switches 37 and 14 are closed the lowest possible voltage is obtainable, (indicated in position lofgthe chart), Whereas when switches 37 and 19 are closed the highest possible voltage is obtainable (indicated in position 23 of the chart). To increase the voltage one-fourthof the voltage between taps, switch 37 is opened (position 2). It will be noted that with switch 14 closed, and all other switches open, the lower half 32 of the auto transformer 22 carriesthe full load To increase the voltage. another To make such change even, switch 15 must close before 38 is 0pened.- .The subsequent change is made by closing switch 38 and ,opening 15, and to make this step even 38 should be closed before 15. It should be noted however, that on position 4 switch 38 might remain .closed without afiecting the voltage obtained. However, this would cause a voltage in the circuit that tends to upon whether the winding 34 or 35 is em- The auxiliary windings 34 cause a circulating current. For this reason switch 38 is shown open in position 4. Further changes may be obtained from the chart.

It is to be observed that each of the windings 34 and 35 are utilized with respective halves of the auxiliary winding 22 to in crease or decrease the voltage of the secondary winding 3. During such operation the halves of the winding 22, when carrying full load current, may be likened to a series transformer into which a voltage is introduced, by the energization of the auxiliary winding 36. When current is flowing in the upper or lower half of the winding 22 an energization of the winding 36 increases or decreases the voltage of the secondary winding 3 an amount that is equal to one-fourth of the voltage between adjacent taps, depending ployed for such purpose.

The invention greatly reduces the number of switches and taps required for Voltage changes in small steps and thereby greatly simplifies existing equipment.

It will be apparent to those skilled in the art that various minor changes may be made in my device without departing from the spirit thereof. I desire that my invention shall be only limited by the appended claims.

I claim as my invention:

1. In combination, a main transformer havmg a primary and asecondary winding, one

of said windings having a plurality of taps,

an auxiliary transformer having a primary and a secondary winding, meansfor connecting said taps alternately to opposite terminals of said secondary winding of said-auxiliary transformer, the mid-point of said secondary winding constituting a terminal for the 5 tapped winding of said main transformer,

and means including two windings energized by said main transformer and switches for connecting the one or the other of said w'indlugs to the primaryiwinding of said auxiliary transformer to increase or decrease the terminal voltage of the transformer with respect to the voltage of the tapped portion of said v winding.

2. The combination with a main transformer having a winding provided with a plurality of taps, a preventive auto-transformer having terminals adapted to be conrelationwith said auxiliary winding.

3. The combination with a main transformer, of means for changing the voltage ratio of said transformer while under load comprising a preventive auto-transformer adapted to have its terminals in circuit rela tion with a portion of the'turns of said winding, its mid-point constituting a terminal for said main transformer, and means for increasing or decreasing the voltage of said last named terminal including two windings energi-Zed by said main transformer and switching means for connecting the one or the other of said windings in circuit.

4. In combination, a transformer having a core, primary and secondary windings on said core, means for changing the voltage ratio between said windings including a preventive auto transformer, taps connected to said secondary winding b means of which said autotransforme'r may e connected in circuit relation with said secondary winding, tap changing apparatus associated therewith, a primary winding on said preventive auto-transformer, and a winding on said main transformer core for energizing said primary Winding.

5. The combination with a transformer having a primary and a secondary winding, said secondary winding having a plurality of taps, a current limiting coil having end terminals that are adapted to be connected through switches to said taps, and a mid terininal constituting a power circuit connection to said secondary winding, of means for changing the voltage ratio between said primary and secondary windings an amount smaller than the voltage ratio change between said taps comprising a winding inductively related to said current limiting coil and switching means for energizing said winding in the one or in the other direction with respect to said secondary winding to increase or decrease the voltage thereof in predetermined steps.

In testimony whereof, I have hereunto subscribed my name this 10th day of July, 1928.

LELAND H. HILL. 

